ORGANS of REPRODUCTION.
THE varieties in the form, structure, and situation of the organs of reproduction in the inferior animals, are so numerous, and so remarkable, that Linnxus once pro posed to extend to animals the sexual system, which he employed for the classification of plants, and was deter red from carrying this plan into execution, only through the fear of offending the modesty of his readers. Vial d'Azyr seems to have favoured this plan of arrangement, when he declares, that these organs would easily furnish characters for such a method.
In a few animals there are no organs by which the functions of generation can be performed. This is the case with the ZOOPHYTES, except those which Cuvicr has called echinodermata. The instances arc still more numerous, in which, though these organs exist, they are the same in each individual of the species, or where there is no distinction of sex. The cchinodermata, most Wonms, and several MoLLusc A, are real hermaphrodites, and have the power of reciprocally impregnating each other, or of generating singly. All other animals have the sexes distinct.
As a sexual distinction of the organs of reproduction is not universal among the interior animals, it will be necessary, in the comparative view which we are here to take of these organs, first to notice their varieties in hermaphrodite animals, and we may then proceed with the male and female organs, according to the arrange ment followed in the corresponding chapter of Human Anatomy.
The organs of reproduction in the cchinodermata, seem to consist merely of ovaries, or collections of ova, which, in some species, as in the common starfish, form, at par ticular seasons, a very conspicuous part of their internal structure. The ovaries of the sea urchin consist of from 5 to 10 considerable bodies of a reddish colour, that lie along the central surface of the shell, and open round the anus. These are said by Cuvicr to be the eatable part of these ZOOPHYTES. • Among the Woams, the leeches, the earth-worms, and a few others, are hermaphrodites, and both these which we have particularized, mutually impregnate each other. In the leeches there is a thick and long muscular tube, which is considered as the Penis; two testes, composed each of numerous folds of a soft whitish canal, and fur nished with an excretory duct that is short, straight, and muscular ; and near these organs there is a cavity open ing outwards, so as to receive the penis of another indi vidual. The generative organs in the earth-worm ap pear, according to Cuvier, to consist of distinct ovaries, and of two peripheral orifices, near the middle of the body that communicate with two or three soft oval pouches of a glandular texture, placed within the cavity of the abdomen. These latter are probably the impreg nating organs ; but there are no evident organs of copu lation.
There is some difference in the accounts given by wri ters on the natural history of intestinal worms, respect ing the sexual organs of the ascarides, found in the hu man intestines. These worms are represented by Wer ner, Tyson, and Dr Baillie, as male and female ; while Cuvier states, that he never saw a male ascaris ; and Dr Hooper affirms, that all the ascarides possess all the parts described, as belonging to the female.
Among the MoLLusc A, snails and slugs are her maphrodites, and their organs of generation arc not a little singular. These are situated in the right side of the neck, below the upper horn, where there is an aper ture, and from this opening, in the breeding season, there is extruded a sort of bag, which contains testes, a penis, and several little horny substances, about half an inch long, and pointed at one end. These have been com pared to darts, and, according to Dr Shaw, are lite rally shot by the animals at each other, previous to co pulation. Besides these bags of darts, which may be called the male organs, each animal has an ovary, situated at the dorsal part of the body, between the lobes of the liver and the intestinal canal, and composed of numerous granular bodies, each of which contains an egg.
The only organs that are universally found in the males of those animals that have a distinction of sex, are the testes. The seminal vesicles are wanting in most of the inferior classes, and sometimes even in MANI ; the prostate gland is not found, even in all those animals that have a urinary bladder, but the pe nis is pretty generally found, especially in the first five classes.
In many of the MAmmtitia, the testes are situated without the cavity of the abdomen, within a scrotum. This bag does not exist, however, in those animals that live much below ground, as in the mole, the shrew; nor is it found in the pachydermata, the civet, the camel, the otter, the hedgehog, and several of the rodentia; in all of which the testes are concealed between the skin and muscles, near the sacro-sternal part of the abdomen. In some species, as the elephant, the ornithorynchus pa radoxus, the hyrax, seals and walruses, the testes con stantly remain within the abdomen. Several animals have the power of withdrawing the glands from the ab domen, and retracting them into that cavity, according to circumstances. This is the case with the hamster (inns cricetus,) and the Canadian musk-rat, (musi zibe thicus.) In all other animals, the testes are concealed within the abdomen. In Blares, they lie near the kid neys, and their excretory ducts terminate near the rec tum, in a dilated part, which was considered by De Graaf as the penis of these animals. See Tract de Mu/. Or gan. p. 216. The testes have a similar situation in REP